The present invention relates to strobe lamp power supply and firing control circuitry and, more particularly, to a circuit providing for series firing of a strobe lamp at high altitudes with increased dependability.
Strobe lamps typically comprise a glass bulb in which are positioned two electrically isolated power electrodes. The bulb is filled with a gas, such as xenon which, when ionized, generates light of high intensity. A power supply provides an electrical potential across the power electrodes of the lamp, which potential is generally insufficient to cause the xenon to ionize. Once the lamp is fired, that is ionization is begun, however, the power supply will provide a large current flow between the power electrodes. A highly reflective metal light reflector is generally positioned adjacent the lamp to reflect the lamp light output in the desired direction.
Various firing techniques have in the past been used with strobe lamps. In a parallel trigger configuration, a high voltage pulse, on the order of 14,000 volts is supplied to the metal reflector. This trigger pulse will cause the gas in the bulb to ionize and the lamp power supply, typically including one or more capacitors, will then discharge through the lamp power electrodes to produce the strobe light flash.
It will be appreciated that raising the metallic reflector to an elevated potential of 14,000 volts will require that the reflector be thoroughly insulated from the surrounding strobe lamp structure which is grounded. While such insulation is possible at low altitudes, it will be appreciated that at high altitudes the insulating effect of the air between the reflector and adjacent grounded conductive parts of the lamp structure is reduced or eliminated such that unwanted arcing to ground from the reflector becomes virtually impossible to prevent.
In high altitude aviation and aerospace applications, it has been found necessary therefore to utilize a series triggering technique for triggering the strobe lamp. In a simple series triggering configuration, the reflector is grounded and plays no part in the triggering process. A trigger transformer has its secondary high voltage coil connected in series with the power supply for the lamp such that a 14,000 volt trigger pulse will be impressed upon the power supply output and applied to one of the power electrodes of the strobe lamp. Power supply voltage is typically on the order of 500 volts. While a simple series triggering technique was found to be operable, although undependable, at sea level, simple series triggering was not practical at high altitudes. It is thought that with one of the power electrodes of the strobe lamp being raised to 14,000 volts, too much leakage between the charged electrode and grounded structure, principally the grounded reflector, occurs. The energy which is leaked to the grounded reflector will not effectively ionize the xenon gas in the lamp. Additionally in a series triggering strobe lamp circuit, the high current discharge through the lamp must pass through the trigger transformer secondary windings. This results in a substantial increase in transformer size and weight which may be highly undesirable in an aviation application.
It is seen, therefore, that a need exists for a simple and reliable power supply and trigger circuit for a strobe lamp which will operate effectively at high altitudes and in which circuit component size and weight are minimized.